Thermodynamic assessment of CaO‐SiO 2 ‐Al 2 O 3 ‐MgO‐Cr 2 O 3 ‐MnO‐Fe t O slags for refining chromium‐containing steels

The slag system of CaO‐SiO 2 ‐Al 2 O 3 ‐MgO‐Cr 2 O 3 ‐MnO‐Fe t O relevant to refining chromium‐containing steels such as bearing steel is thermodynamically assessed at 1873 K. The activity coefficient of Fe t O shows an initially rapid increment followed by a gradual reduction according to Cr 2 O 3 content at a constant basicity, and decreases with increasing slag basicity. γ MnO is decreased abruptly by increasing Cr 2 O 3 content and thereafter, maintains a nearly constant level. From the standpoint of inclusion control, the Cr 2 O 3 presence in ladle refining slags is thermodynamically harmful in that it minimizes the inclusion level by inducing the increment of γ Fe t O even though Cr 2 O 3 exists in extremely small amounts. However, it is beneficial in that it diminishes AI reoxidation by decreasing γ MnO . The presence of carbon in slag decreases γ Fe t O and γ MnO , which turns out to be favourable for the reduction of Al reoxidation. The thermodynamic equilibria of chromium and manganese are quantified in terms of Fe t O and Cr 2 O 3 content as well as slag basicity by using multiple regression analysis. L Cr and L Mn are increased by the presence of Cr 2 O 3 , indicating a low recovery efficiency of Cr and Mn in the treatment of ferroalloy addition. In determining L S values, Cr 2 O 3 is not so important as the basicity of slags.